075 stihl building pressure in fuel tank

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AKDoug

AKDoug

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Modern Stihl serial numbers are 9 digits long. If it isn't a 9 digit number, I don't believe it is traceable outside of contacting Stihl directly.
 
Kfd518

Kfd518

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Got is thank you sir for the clarification. Blue mountain states they have no way to track it being as it was sold originally way out of their service area
 
Kfd518

Kfd518

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Still waiting for oil pump worm oil seal to come in…stihl 9642-003-1440 backordered from stihl as well as the anti vibe mounts under the handle assy. 2-3 week availability 1.5 weeks down can't re-test till it get is hopefully this is the problem. Went ahead And replaced fly wheel side and clutch side main oil seals while in there.
 
Kfd518

Kfd518

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Don’t know what finally cured it. It got taken down to crank case halves and shaft. Both seals replaced. Base gasket replaced carb rebuilt again and all other seals replaced. Now tight to pres and vac. Runs like a top. Sorry I’m not much more help I’m thinking the lean out as well as crappy summer blend fuel was causing it to boil
 
Willeywoodcutter

Willeywoodcutter

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My saw doesn't boil the fuel but seems like it is building pressure to the point you have to start it with the throttle locked. I was wondering about the fuel cap what is that little screw for do you know? Thanks for the quick reply too
 
Kfd518

Kfd518

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Tank vent is there. Sounds like it’s running rich and flooding out to me if you have to lock the throttle. Check your adjustments likely low side, or could be that low side is completely clogged and not passing fuel but if this is the case it shouldn’t idle at all. I may be wrong in my assumptions though.
 

SEAM

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The tank vent should optimally let air in but no fuel out. Pressure build-up in the tank is quite normal and the inlet needle in the carb should be able to cope with that. The older vent systems usually were not perfect - some even start to "bubble" around the vent with a full tank - and did not cause an overly build-up of pressure.
I would check if the inlet needle (below the metering valve/lever) holds (some) pressure. If it leaks pressure building up in the tank will push fuel through the carb when the saw is not used due to changes in ambient temperature.
The venting action can be checked using a piece of hose directly on the vent holes in the cap.
 
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